1. Field of the Invention
This invention relates to an adhesive for sealing the primer cup ring in center fire ammunition.
2. Brief Description of Related Technology
Anaerobic adhesives are known, as are anaerobic adhesives having a secondary cure mechanism, such as ultraviolet curing. Such adhesives are widely used commercially. Nonetheless, certain commercial applications have proven troublesome for those anaerobic adhesives and UV/anaerobic dual cure adhesives.
For instance, in one such commercial application, ring sealing the primer cup in the cartridge of center fire ammunition, plasticizers are used in the adhesive to provide a flexible adhesive joint at the ring seal to absorb trigger impact. In this application, the primer cup, when inserted into the cartridge case, cures by virtue of the anaerobic cure mechanism. The seal around the primer cup, which is exposed to the atmosphere, is cured by irradiation with UV light. The sealing function is to prevent the ingress of atmospheric or other moisture into the primer cup that is filled with a lead-free organic compound, but tends to be hygroscopic in nature. A primer seating defect can result in the misfiring of a gun.
However, these plasticizers tend to leach out of the adhesive bond leaving a sticky residue on the ammunition cartridge surface. With UV/anaerobic dual cure products, plasticizers used may become entrapped and thus do not leave a sticky surface. In addition, the integrity of the ring seal may become compromised leading to failure and separation from the ammunition cartridge surface. This is problematic after ammunition is fired as the gun barrel may become clogged.
Radiation curable anaerobic adhesive compositions are known. For instance, U.S. Pat. No. 4,533,446 (Conway) is directed to such a composition that includes an anaerobically curable monomer, cationic photoinitiator, a peroxide and a ferrocence-based anaerobic polymerization initiator. However, in practice, these compositions have poor pot life since the metal ion in the ferrocene compound acts to initiate anaerobic cure.
It would be desirable to provide an anaerobic adhesive, which may or may not cure through a secondary mechanism, that does not suffer from these recognized shortcomings.
The present invention provides UV/anaerobic dual cure adhesives, particularly well-suited for sealing the ring around the primer cup (i.e., the primer cup/primer pocket interface) in center fire ammunition by UV cure and the primer cup in the cartridge by anaerobic cure.
More specifically, the adhesives include a (meth)acrylate component, at least a portion of which is a monofunctional (meth)acrylate; an anaerobic cure-inducing component; and a photoinitiator component, where the monofunctional (meth)acrylate is present in an amount in the range of about 10 to about 25% by weight of the total composition. The adhesives may also include a plasticizer component in an amount less than about 20% by weight of the total composition.
The invention is also directed to a method of making such compositions, as well as a method of using them. For instance, the invention provides a method of using the compositions in the assembly of ammunition, such as the primer sealer.
In addition, the invention provides cured reaction products of these compositions.